Orion Nebula

Using A Canon 300mm Lens for Astrophotography

If you watched my video about Comet 46P Wirtanen, you may have noticed that my imaging gear included a Canon EF 300mm F/4L USM Lens. This may have seemed a little odd to those that are used to seeing me use a telescope for astrophotography, but a camera lens like this can be a great way to capture deep sky images.

Over the years, a lot of people have asked me why they should invest in a new telescope when they already own a high-quality telephoto camera lens with a comparable focal length. After all, a prime lens like the Canon EF 300mm F/4L isn’t cheap, and its got some seriously impressive optics.

So, if you’ve already got a lens like this in your kit, you should definitely try using it for astrophotography before investing in a new telescope.

Canon 300mm F/4L Lens for Astrophotography

Make no mistake, a telescope designed for deep sky astrophotography has many advantages in terms of deep sky astrophotography. Specialized features such as a robust dual speed focuser, light baffles, and the ability to easily accommodate astronomy cameras and autoguiding systems to name a few.

But if you’ve been into photography for a while, there’s a good chance you’ll already own some camera lenses that are perfect for astrophotography. The secret is, to leverage the tracking abilities of an equatorial mount that allows you to capture long exposure images of the night sky without star trailing.

In this post, I’ll show you how I managed to capture an impressive portrait of the Orion Nebula using a 300mm camera lens from my backyard in the city. I’ll discuss the filter I recommend, the camera settings I use, and the share the process of capturing long exposure images on a tracking mount.

My Canon EF 300mm F/4L USM Lens

Canon 300mm F/4L (Non IS)

The camera lens I am using is a first generation Canon EF 300mm F/4L (Non-IS). This is an old L-series lens from Canon that does not include Image Stabilization, but does include the ring type USM autofocus motor. Features like IS and autofocus won’t work for astrophotography, so older prime (non-zoom) lenses like this are a great value in the used market.

It’s quite useful to have prime lenses at different focal lengths in your astrophotography kit. You’ll be able to capture a wide variety of targets from large open star clusters to emission and reflection nebulae like Orion. (See my review of the Rokinon 135mm F/2 for even wider deep sky images).

Video: Deep Sky Astrophotography with a 300mm Camera Lens

I purchased my 300mm F/4L used, and drove a fair distance to meet the seller. The lens was originally intended for bird photography, which I still enjoy today with a 1.4 extender attached for more reach. The native focal length of 300mm and widest aperture are a better configuration for astrophotography purposes.

The 1.4 x Canon teleconverter introduces chromatic aberration, and I lose a full stop of light (F/5.6). This is not usually an issue in my daytime photography images, but it’s out of the question when photographing stars.

Using the Canon 300mm F/4L lens on a crop-sensor DSLR (APS-C) camera like my Rebel T3i will effectively create a narrower field of view than a full-frame camera does. This creates an equivalent focal length of 480mm with the crop factor applied (1.6X), which is important to consider when framing up an astrophotography target.

Using a simple FOV (field of view) calculator, you can get a preview of the expected image scale of your target. As you can see, the Canon 300mm F/4L and Canon EOS 600D combo frame the Orion Nebula and Running Man nicely.

The Field of View using a 300mm Camera Lens and APS-C Sensor DSLR

Most of the astrophotography telescopes I recommend for beginners hover around the 400mm to 700mm focal length mark, so this camera lens is quite comparable. Also, the Canon EF 300mm F/4L Non IS contains two UD (Ultra low dispersion) lens elements similar to the construction of an apochromatic refractor.

The rather fast optics of this lens (F/4) is advantageous for night photography, as its widest aperture will allow plenty of signal (light) to be collected in each shot. For comparison, my Sky-Watcher Esprit 100 APO has an F-Ratio of F/5.5.

When it comes to acquiring astrophotography data for a healthy signal to noise ratio, a camera lens with a fast aperture is recommended. This is why camera lenses like the Rokinon F/2.8 and Canon F/1.8 are excellent choices for astrophotography.

Focusing the lens

Finding a precise focus using a camera lens is much more difficult than it is with a telescope. Rather than using a smooth dual-speed micro focuser, you have the challenging task of using the rather sensitive focusing ring on the lens (in manual mode of course).

It’s best to point the camera towards a bright object (not a star) to find the initial focus. The Moon, or a distant streetlight will do. Once you have it dialed in using the lenses widest aperture (F/4), you can then aim the lens at a bright star in the night sky using your cameras highest ISO setting.

From here, it’s a matter of trial and error until you find the sweet spot. Once you’ve found it, be very careful not to bump it out of focus when slewing to your target. You can always fine tune the focusing ring on your deep sky target using short test exposures after.

The Camera: Canon EOS Rebel T3i

This Rebel T3i (600D) camera has been “modified” for astrophotography, which isn’t nearly as complicated or technical as it sounds. I’ve basically removed an internal filter that blocks certain wavelengths of light from being recorded on the sensor (I didn’t modify this 600D myself, it was done by a professional).

The stock internal IR cut filter found in DSLR cameras like the Canon Rebel T3i creates “normal” looking daytime images, but can hold your astro images back. If you own a DSLR camera that you want to use for astrophotography, look into getting it modded. I waited almost 4 years before making this upgrade, and it significantly improved my astrophotography images.

This modification will better showcase the rich areas of hydrogen gas in the Orion Nebula. For certain deep sky targets (such as the California Nebula) a full-spectrum modified DSLR is essential for a respectable image.

My Full Spectrum Modified Canon EOS Rebel T3i

The Orion Nebula isn’t one of them! A stock DSLR camera can capture exquisite images of this reflection/emission nebula with beginner-level equipment.

To photograph Messier 42, I’ll shoot a series of 1.5-minute exposures at ISO 400. The images will collect a healthy amount of signal (or light) on this nebula and the surrounding area. With the temperature hovering around zero on the night of acquisition, I benefited from a cool camera sensor that didn’t produce nearly as much noise as I experience in the summer.

Covering the sensor is an Optolong L-Pro filter. This broad spectrum filter is an excellent choice if you are looking to produce natural looking astrophotography images in the city. Light pollution is a big problem for many amateur astrophotographers, and filters like the L-Pro can make your life easier.

This filter clips-into the camera body, and fits neatly underneath the camera lens. Being able to use this filter with either a camera lens or telescope attached is a real bonus. I have also used this filter underneath the Rokinon 14mm F/2.8 lens for some wide angle shots of the night sky from home.

The Camera Mount: iOptron SkyGuider Pro

The iOptron SkyGuider Pro is the perfect solution for those looking to get started in astrophotography with a DSLR camera and lens. It’s a highly portable, non-nonsense astrophotography mount that allows you to start tracking the movement of the night sky for long exposure imaging.

With the counterweight attached, it can handle heavier lenses like this 300mm F/4L, and even a small telescope like the William Optics Z61.

For this mount to be effective, it must be accurately polar aligned. In the northern hemisphere, we have the advantage of being able to use the north star, Polaris, to help us align with the polar axis of the Earth.

The iOptron SkyGuider Pro Camera Mount

To start tracking, its a simple as turning the SkyGuider on, with the mode set to 1X sidereal rate. After that, the camera mount slowly matches the apparent rotation of the night sky, and my long exposure images record pin-point stars without trailing.

The SkyGuider pro includes an illuminated reticle that you can use as a guide to align the mount. This make it really easy to get your alignment just right – which is critically important for astrophotography. Polar alignment and balance will make the biggest impact on your images.

The farther off you are in either area (balance and polar alignment), the shorter your exposure times will need to be. With a sound polar alignment and a careful balance, unguided exposures of 3 minutes or more are no problem on the iOptron SkyGuider Pro mount.

Locating Objects with the SkyGuider Pro

To locate and frame a deep sky target using this mount, it must be done manually (no GoTo functionality). For bright targets like the Orion Nebula, this is extremely easy, as I can line up the target using the viewfinder on my DSLR camera. For faint targets, or when using a narrowband filter, you may need to take a number of test exposures to get it framed just right.

I personally have the SGP mounted to a lightweight carbon fiber tripod. This is a highly portable configuration, but it’s likely a little too flimsy for folks that want a rock-solid platform. Consider using a more robust aluminium tripod with this mount.

The Target: Orion Nebula

The bright moon certainly isn’t helping me capture the faint dusty details surrounding Orion. Luckily, M42 is such a bright deep sky object that it can be enjoyed in less than perfect conditions. I’ve photographed this target so many times, and it never gets old.

It’s a spectacular target to test new equipment on, because you are bound to get a rather impressive image no matter which approach you take. The light pollution filter used (Optolong L-Pro) did a great job of reducing the unwanted artificial light present in my backyard, allowing the natural star colors to shine through.

To create my final image, I’ve stacked the individual exposures together using a free software called DeepSkyStacker. The resulting was then brought into into Adobe Photoshop for further processing. If you want to learn how I process my astrophotography images, have a look at some of the image processing tutorials I’ve shared in the past.

Image Details

The Bottom Line

As you can see in my image above, the stars are sharp and free of chromatic aberration (color fringing). This is a testament to the high quality optics of the 300mm F/4L lens, and an important factor to consider when choosing a camera lens for astrophotography.

Capturing sharp, accurately colored stars is the ultimate challenge for optical equipment, and the Canon EF 300mm F/4L passes with flying colors. The field is also extremely flat, another trait of only the best camera lenses.

A prime telephoto camera lens like the Canon EF 300mm F/4L is a great way to capture deep sky astrophotography images, as long as you’ve got a way to track the night sky for each shot. The wide field of view is very forgiving, meaning autoguiding isn’t necessary for a successful long exposure image.

Whether you’re using a camera lens, telescope, or a pair of binoculars. I hope you’re able to get out and appreciate the impossibly beautiful history of our universe that shines above our heads this season.

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Capturing Orion with a Fluorostar 132

I have recently had the incredible opportunity to try out an enormous 132mm refractor telescope for some deep sky astrophotography. Connecting a DSLR camera to a telescope like this is something I never dreamed I would have the pleasure of doing.

This is as good as it gets for fans of the apochromatic refractor telescope design. The William Optics Flourostar 132is an F/7 triplet apochromatic refractor, designed to deliver superior deep-sky astrophotography performance. The massive 132mm objective lens means that it collects light from objects in space at an impressive rate, which can then be recorded by the sensor in your DSLR camera.

With a limited window of clear skies available at this festive time of year, choosing a target that delivers satisfying results in a short period of time is worthy of some thought. After some deliberation, I ended up shooting quite possibly the most widely photographed DSO’s on the planet. Go figure!

The Orion Nebula (and Running Man Nebula)

My image is comprised of about 1 hour worth of total exposure time using a Canon EOS Rebel T3i camera at ISO 800. The camera had a SkyTech CLS-CCD clip-in light pollution filter to reduce the city glow present in my backyard sky. Shorter exposures of 15-seconds and 30-seconds were added to capture the bright core of M42.

In true-color broadband photos, the outer nebulosity and details of M42 can be hard to pick up without soaking in some serious time under the stars. As you can see in the image, much of the outer hydrogen gas was captured in a short period of time.

The Running Man Nebula (Sh2-279) is also shown to the left of Orion, which is a combination of a number deep sky objects. An open star cluster, emission nebula, and a reflection nebula to name a few. Those of you shooting with a wide FOV should consider including this object in your portrait of the area.

I have photographed the Orion Nebula many times using various focal lengths. In my opinion, wide-field apochromatic refractors like these produce the most dynamic images of this region.

The Fluorostar 132 is by far the most impressive telescope I have ever used, period.

The sheer size of this telescope can be hard to fully understand without a sense of scale. The gold accents that decorate this flawless white tube are a fitting choice considering the prestige of using the FLT 132.

If you can handle the extra weight, the imaging performance of a refractor of this size is unmatched. Color correction, contrast, and clarity are all benefits of an apochromatic refractor. The triplet lens design and dedicated field flattener mean that the stars in your images are razor sharp points of light to the edge of the frame.

At almost 20 lbs (without photography gear) the Fluorostar requires a heavy-duty equatorial mount to enjoy. Keep reading for a detailed description of this dream ‘scope.

My image of the Orion Nebula used short exposures (2 minutes each) at a modest ISO 800, yet revealed the faint details of M42 usually only seen in much longer exposures. I am curious to see the amount of detail acquired when shooting ultra-long narrowband exposures with a cooled camera.

I was pleased to see the field of view in this refractor is still quite wide, considering its longer focal length of 925mm. Medium-sized targets such as the Orion Nebula fit nicely in the image frame using a crop-sensor camera body such as a Canon EOS Rebel DSLR.

Astrophotography with a giant refractor telescope:

Watch me shovel snow so I can set up my imaging equipment for a cold night under the stars! The weekend ended up clouding over completely, so it was my one and only chance to test the Fluorostar. Despite having a cooled CMOS camera in my possession at the moment (ZWO ASI294MC Pro), I opted to test the DSLR astrophotography performance of the FLT 132.

The act of capturing deep sky images with an affordable DSLR camera will never lose its appeal. It’s where my journey began, and I will continue to shoot this way for years to come.

My Canon EOS Rebel T3i connected to the Flattener/Reducer using the William Optics 48mm T-Mount

A flagship telescope from William Optics

The William Optics Fluorostar 132 (FLT 132) is ideal for astrophotography due to the FPL-53 glass objective lens. This is a top of line material used in only the finest refractor telescopes. You may remember my review of the William Optics Zenithstar 61 APO, which also used this glass. The deep-sky imaging performance of that little APO is what sparked my interest in the Fluorostar.

Using a William Optics Telescope is something that can only be described as a luxury experience. Every last detail of these telescopes has been carefully designed and implemented to improve the overall astrophotography experience. The small details that are only noticed when you experience a night of astrophotography with a product like this left a lasting impression on me.

You can not deny the beautiful aesthetics of a William Optics telescope. When you invest in a tool that allows you to take incredible photos of objects in space, it holds a special place in your heart. Refractors like the FLT 132 reflect this admiration for the hobby and stand as a symbol of technological advancement in performance and design.

William Optics Fluorostar 132 F/7 Triplet

The packaging of the FLT 132 included a soft carrying case with a thick padded liner. The William Optics logo and name were stitched in a vibrant orange color to the front of the case, and the big bag included heavy duty straps to easily transport the precious cargo inside.

The tube rings, mounting plate, and lens cap are all finished in a luxurious gold color. When I first saw this telescope, all I could think of was that the FLT 132 was designed for a king. William Optics provided me with absolutely everything I needed to get up and running my first night. From the screws needed to mount the 50mm guide scope, to the impressive Flattener 7 dedicated field flattener, the attention to detail from this company is both appreciated and enjoyed.

Dedicated Field Flattener

The dedicated field flattener/reducer for the Fluorostar 132 is the Flattener 7. Its a large, beautiful, color matched accessory for the Flurostar, that connects your DSLR camera to the 3-inch focuser on the 132. The reducer threads directly into the focuser drawtube, and brings your camera view back to 740mm with the 0.8X reduction.

This is definitely the most aesthetically pleasing flattener/reducer I have ever used. The color matched gold adapter ring completes the color coordination for the entire rig. It’s quite a sight!

Full-frame DSLR owners will be happy to know that your image sensor will be completely exposed through the large image circle.

The Image: The Orion Nebula

My image is comprised of about 1 hours worth of total exposure time using a Canon REOS Rebel T3i camera at ISO 800. The camera had a SkyTech CLS-CCD clip-in light pollution filter to reduce the city glow present in my backyard sky. Shorter exposures of 15-seconds and 30-seconds were added to capture the bright core of M42.

The amount of detail captured in each 2-minute sub at ISO 800 was impressive. The giant 132m aperture of this telescope at F/7 can pull in a lot of light in a short period of time. Each set of images were stacked separately in DeepSkyStacker and then combined in Photoshop.

Photo Details

Captured using BackyardEOS
Stacked in DeepSkyStacker
Processed in Adobe Photoshop

I captured 30 x 15-second exposures to properly expose the core of the Orion Nebula

Imaging Session Challenges

I hoped to gather at least 2-3 hours worth of exposure time on the Orion Nebula with my Canon T3i, but balancing issues plagued my imaging session. The new weight of the FLT 132 with my imaging gear attached was a brand new configuration for me on the iOptron CEM60.

This meant that I needed to properly balance a load of nearly 20 lbs in both the Declination and Right-Ascension axis. I found an acceptable balance of the telescope before attaching the DSLR, and hoped the balance would remain stable once the photography gear and focus distance were applied. Unfortunately, the focus draw tube needed to be extended much further than anticipated, and this added backend weight through off my initial balance.

The good news is, I marked this position and now know exactly where to place the imaging train when balancing the load next time.

William Optics 50mm Guide Scope

Finding focus with my autoguiding camera and a new guidescope took some time as well. I mistakenly thought that an extension tube was needed to find focus using the William Optics 50mm Guide Scope. The stars in my Altair GPCAM2 AR0130 Mono came to focus when I inserted the camera directly up against the rotolock adapter on the guidescope. This is the best-case scenario, as it keeps the autoguiding setup compact and cables are out of the way.

FLT 132 Telescope Specifications

What’s Next?

This year was full of new astrophotography adventures both in the backyard and beyond. I had the opportunity to try several new cameras, mounts, and filters thanks to my partnership with Ontario Telescope & Accessories. I have a number of deep-sky imaging products just waiting to be tested and reviewed on the YouTube Channel.

Update: I captured this image of the Horsehead Nebula using the FLT 132 on January 20, 2018. This image is comprised of 40 x 3-minute subs at ISO 800, using a modified Canon 600D DSLR.

I look forward to sharing another exciting year of astrophotography with you all. For me, 2017 was full of surprises with some ups and downs. The one thing that remained constant was my unwavering love for the night sky and joy of sharing my experiences in the backyard with you.

My journey through the hobby of deep-sky astrophotography continues to take me to new places and provides unforgettable experiences along the way. Happy Holidays and best wishes for the New Year!